1. Field of the Invention
The present invention generally concerns swage mounting and swage mounted assemblies, such as swage mounts used to connect components used in an actuator arm assembly for a computer hard disk drive.
2. Description of the Prior Art
Swage mounting is used in a wide variety of fastening applications, particularly where assembly cost and height profile are important considerations. One important use of swage mounting is in the construction of disk drives.
Disk drives are used in a variety of devices such as computers, facsimile machines, copiers and any other equipment where mass digital data storage is desired. Two important and costly sub-assemblies in disk drives are a head gimbal assembly (HGA) and a controller driven actuator assembly, referred to as a head stack assembly (HSA). An HSA comprises one or more HGAs, an actuator body, a coil and a bearing. Included in the HGA is a read/write head that is capable of reading digital information stored on platters in the disk drive. The HSA precisely positions the read/write head vertically adjacent a precise point on the disk drive platter, with the actuator directing the movement of the HGA across the face of the platter. Each HGA includes precision-made components manufactured to exacting standards. Because of the complexity involved in each HGA, manufacturers have found that having the ability to disconnect and reconnect the HGA from the HSA substantially reduces costs should either assembly require rework or replacement.
To facilitate the cost-effective repair and/or replacement of these assemblies, the HGA and HSA are typically connected at a stacked joint defined by the distal end of the pivoting actuator arm and the proximal end of a thin elongated load beam. The opposite end of the load beam supports the read/write head that sweeps across the disk platter in response to an actuator controller. Satisfactory operation of the drive requires the read/write head to be selectively positioned vertically adjacent to selected annular data tracks formed on the platter within response times on the order of milliseconds. Such response involves high levels of acceleration. In the event of the actuator accidentally contacting the crash stop during seek, the acceleration levels can reach levels of several hundred Gs. To determine the torque exerted upon the swage mount connection during a crash stop or seek event, the worst case assumptions are made. A conservative estimate for an HGA mass is 100 mg (only the portion extending from the swage mount), with a centroid located 5.6 mm from the swage mount boss centerline. A nano slider (6 mg) typically is located 18 mm from the boss centerline. Using these assumptions, the torque exerted upon the swage mount is at most 0.0007 N*mm/m/s2[0.00171 in-oz/G]. Thus, if a 1000G shock event occurred, the resulting torque exerted on the swage mount would be 1.7 in-oz.
During the hard disk drive assembly process, there are several steps which involve placing the HSA in various fixtures and machines. A lateral force of 100 grams (0.22 lbs) on a load beam at a distance of 15 mm (0.59 inch) from the boss centerline results in a torque of 14.7 N-mm (3.8 in-oz). Therefore, the fastener connecting the actuator arm to the load beam must have the capability to withstand considerable torque, on the order of 4-5 inch-ounces or more.
Disk drive manufacturers continually endeavor to reduce the size of their disk drives to meet market demands for faster drive operating speed and increased storage capacity. To increase storage capacity, additional double-sided platters are vertically stacked with each platter having its own HGA. However, adding platters to a disk drive has the undesirable effects of increasing the vertical profile of the drive, increasing component cost and impairing component reliability. As a result, manufacturers have endeavored to miniaturize existing drive components.
One such method for reducing the overall drive size is to reduce the size of the stacked vertical joint connecting the HGAs to the HSA. For example, in U.S. Pat. No. 5,689,389 (Braunheim ""389), the contents of which are incorporated herein by reference as though set forth herein in full, a low profile swage mount fastener is used to connect the load beam of the HGA to the actuator arm of the HSA. Because the swage mount fastener has a low profile, the overall height of the disk drive may be reduced, especially in drives using multiple platters and HGAs. However, a disadvantage of using a low profile swage mount fastener is that as performance demands increase, it provides less torque retention than is required to withstand the force levels imposed on the load beam during drive assembly and during shock events.
In Braunheim ""389, the torque retention characteristics of a low profile swage mount fastener were increased by modifying the internal geometry of the swage mount. However, the level of torque retention that can be achieved solely by modifying the swage mount design is limited. Without increased torque retention values, the shock-driven acceleration rate a load beam can withstand is limited, which imposes an upper limit on the robustness of the drive package and handling constraints on the drive assembly processes. Accordingly, there is a shortcoming in the art in the unavailability of a low profile swage mount fastener capable of torque retention values that are significantly higher than have been previously achieved.
Moreover, as a platter is accelerated the read/write heads begin to fly, forming an air bearing between the head and the platter. For optimal performance, fly height above the platter must be controlled very tightly, e.g., to between 0.5 and 2 microinch (xcexc inch). If the head moves too far away from the platter, drive read/write operations are adversely affected. To accomplish the required control, the load beam portion of the HGA is xe2x80x9cpre-loaded,xe2x80x9d that is, it is biased toward the platter. In pre-loading, the load beam is curved downwardly, such that the read/write head is biased toward the platter. Pre-loading thus creates a downward force on the head so that during drive operation this downward force balances the air bearing and therefore restrains the head from moving away from the optimal height above the platter. Generally, pre-loading of 20 to 40 mN (2 to 4 grams) of force is sufficient to achieve this result. The goal of pre-loading is to achieve an appropriate balance such that the head is close enough to the disk to be able to accurately read data but not so close that the head physically contacts the disk
A present drawback in using a swage mount fastener to join the HGA to the HSA is that the process of swaging causes xe2x80x9cgram change,xe2x80x9d i.e., it changes the delicate balance achieved through pre-loading. The effect swaging has on gram change is measured by comparing the pre-swage gram load of the HGA when loaded to operating height versus the post-swage gram load. It has been found that an average gram change of about 20 to 100 milligrams (mg) occurs as a result of the swaging process. Accordingly, it would be desirable to provide a low profile swage mount fastener in which gram change could be reduced while increasing torque retention values.
The present invention addresses these problems by providing components that are specially adapted for better swage mounting and by providing various techniques that can be used in the manufacture of such components.
Swage Mounting Using Increased Surface Hardness
The present invention addresses the problems in the prior art by providing a swage mounting component that has a hardened surface. In this manner, improved torque retention characteristics often can be achieved. More specifically, this aspect of the invention generally concerns swage mounting and swage mounted assemblies, such as swage mounts used to connect components used in an actuator arm assembly for a computer hard disk drive.
Thus, the invention is directed to a component for use in swage mounting that includes a base plate, having a first side and a second side, and a hub which preferably is cylindrically shaped. The hub extends from the second side of the base plate, and has an inner surface, an outer surface and a core portion disposed between the inner surface and the outer surface. It is a feature of this aspect of the invention that the outer surface of the hub is at least 20 hardness Vickers harder than the core of the hub. Preferably, the component is a swage mount for connecting a disk drive actuator arm to a disk drive load beam.
In preferred embodiments of the above: the hub is comprised primarily of stainless steel, such as 300 series stainless steel or austenitic stainless steel; the outer surface of the hub has been hardened by a mechanical method, a bead blasting method, a heat process, a carburizing method or a nitriding method; the hub is primarily comprised of a base material, and the outer surface of the hub is plated with a second material which is different than the base material; the hub is cylindrically shaped and has a central axis that is perpendicular to the second side of the base portion; the component is a swage mount for connecting a disk drive actuator arm to a disk drive load beam; the first side of the base plate includes an opening, and the inner surface of the hub substantially coincides with the opening in the first side of the base plate; and/or the outer surface of the hub is at least 30 hardness Vickers harder than the core of the hub.
The invention also is directed to a swage mounted assembly that includes a first component and a second component. The first component includes a base plate, having a first side and a second side, and a hub that extends from the second side of the base plate and has an inner surface and an outer surface. The second component includes an opening having an inner surface that is slightly larger than the outer surface of the hub, such that the hub can be received within the opening in the second component. At least one of the following conditions is satisfied: (1) the outer surface of the hub is at least 20 hardness Vickers harder than the core of the hub and (2) the inner surface of the opening in the second component is at least 20 hardness Vickers harder than the core of the second component.
In preferred embodiments of the above: the hub is comprised primarily of stainless steel, such as austenitic stainless steel; the at least 20 hardness Vickers hardness differential has been achieved by performing a carburizing process, a nitriding process, a laser surface hardening process, or a process of plating with a material which is different than an underlying base material; the hub is cylindrically shaped and has a central axis that is perpendicular to the second side of the base portion; one of the first component and the second component comprises one of a disk drive actuator arm and a disk drive load beam; and/or at least one of the following conditions is satisfied: (1) the outer surface of the hub is at least 30 hardness Vickers harder than the core of the hub and (2) the inner surface of the opening in the second component is at least 30 hardness Vickers harder than the core of the second component.
By virtue of the foregoing arrangements, the torque retention characteristics of the swage mount typically can be increased during swage mounting. As a result, the internal geometry of the swage mount typically can be modified to improve gram change characteristics and/or to reduce the mass of the swage mount.
Swage Mounting Using Surface Protrusions
The present invention also addresses the foregoing problems by providing a swage mounting component that includes surface protrusions. In this manner, improved torque retention characteristics often can be achieved.
Thus, in one aspect, the invention is directed to a component for use in swage mounting that includes a base plate, having a first side and a second side, and a hub which preferably is cylindrically shaped. The hub is primarily comprised of a first material (such as stainless steel), extends from the second side of the base plate, and has an inner surface and an outer surface. The outer surface of the hub includes numerous protrusions that are less than approximately 50 microns in height and that are primarily comprised of a second material (such as a carbide or a nitride) which is different from the first material.
In a further aspect, the invention is directed to a component for use in swage mounting that includes a base plate, having a first side and a second side, a hub which preferably is cylindrically shaped. The hub is primarily comprised of a base material (such as stainless steel), extends from the second side of the base plate, and has an inner surface and an outer surface. The outer surface of the hub includes numerous protrusions that are less than approximately 50 microns in height and that are substantially harder (such as at least 50 hardness Vickers harder) than the base material. Such protrusions might, for example, be comprised primarily of a nitride or a carbide.
In a still further aspect, the invention is directed to a component for use in swage mounting that includes a base plate, having a first side and a second side, and a hub which preferably is cylindrically shaped. The hub extends from the second side of the base plate and has an inner surface and an outer surface. The outer surface of the hub includes numerous protrusions that are from 0.5 to 50 microns in height. The component might, for example, be a swage mount for connecting a disk drive actuator arm to a disk drive load beam.
In a still further aspect, the invention is directed to a swage mounting assembly that includes a first component and a second component. The first component includes a base plate, having a first side and a second side, and a hub extending from the second side of the base plate and having an inner surface and an outer surface. The second component includes an opening having an inner surface that is slightly larger than the outer surface of the hub, such that the hub can be received within the opening in the second component. According to this aspect of the invention, at least one of the following conditions is satisfied: (1) the hub is comprised primarily of a first material and the outer surface of the hub includes numerous protrusions that are less than approximately 50 microns in height and that are comprised of a second material which is different from the first material; or (2) the second component is comprised primarily of the first material and the inner surface of the opening in the second component includes numerous protrusions that are less than approximately 50 microns in height and that are comprised of the second material.
In a still further aspect, the invention is directed to a swage mounted assembly that includes a first component and a second component. The first component includes a base plate, having a first side and a second side, and a hub extending from the second side of the base plate and having an inner surface and an outer surface. The second component includes an opening having an inner surface that is slightly larger than the outer surface of the hub, such that the hub can be received within the opening in the second component. According to this aspect of the invention, at least one of the following conditions is satisfied: (1) the hub is comprised primarily of a base material and the outer surface of the hub includes numerous protrusions that are less than approximately 50 microns in height and that are substantially harder than the base material; or (2) the second component is comprised primarily of the base material and the inner surface of the opening in the second component includes numerous protrusions that are less than approximately 50 microns in height and that are substantially harder than the base material.
In a still further aspect, the invention is directed to a swage mounted assembly that includes a first component and a second component. The first component includes a base plate, having a first side and a second side, and a hub extending from the second side of the base plate and having an inner surface and an outer surface. The second component includes an opening having an inner surface that is slightly larger than the outer surface of the hub, such that the hub can be received within the opening in the second component. According to this aspect of the invention, at least one of the outer surface of the hub and the inner surface of the opening in the second component includes numerous protrusions that are from 0.5 to 50 microns in height.
By utilizing surface protrusions in any of the foregoing arrangements, the torque retention characteristics of the swage mount typically can be increased without negatively affecting other properties of the swage mount, such as impairing plastic deformation. As a result, the internal geometry of the swage mount typically can be modified to improve gram change characteristics and/or to reduce the mass of the swage mount.
Carburizing Techniques
The present invention also addresses the foregoing problems in the prior art by providing carburizing techniques that can be used to more efficiently produce components for use in swage mounting, as well as various other types of components. More specifically, this aspect of the present invention generally concerns carburizing techniques, such as carburizing techniques for surface hardening a metal component.
Thus, the invention is directed to carburizing metal. Initially, a furnace is filled with a carburizing gas mixture consisting of a carbon-rich gas and a carrier gas that is lighter than air, and the furnace is heated to a carburizing temperature of at least 1600xc2x0 Fahrenheit. Next, a piece of metal is placed into the furnace while the furnace is heated to the carburizing and filled with the carburizing gas mixture. Thereafter, the piece of metal is removed from the furnace. Preferably, the carrier gas is non-endothermic and/or a reducing gas. More preferably, the carrier gas consists primarily of hydrogen.
In preferred embodiments of the above: the carrier gas is non-endothermic; the carrier gas primarily comprises a reducing gas; the carbon-rich gas is comprised primarily of methane; the carrier gas is comprised primarily of hydrogen; the non-endothermic carrier gas is essentially all hydrogen gas; the piece of metal moves through the furnace on a continuous belt; the furnace is a humpback furnace; the piece of metal remains in the furnace for 5 to 15 minutes; the carburizing temperature of the furnace is not greater than 2000xc2x0 Fahrenheit; the piece of metal has a transformation temperature above which annealing occurs and below which stress relief occurs, and the carburizing temperature of the furnace is not less than the transformation temperature of the piece of metal; the carburizing gas mixture is controlled such that the carbon-rich gas accounts for 2 to 4% of the mixture by mass; the piece of metal is a swage mount; and/or the swage mount is for use in a hard disk drive HSA.
The invention also is directed to carburizing a piece of metal that has a transformation temperature above which annealing occurs and below which stress relief occurs. Initially, a furnace is filled with a carburizing gas mixture consisting of a carbon-rich gas and a carrier gas comprised primarily of hydrogen gas, and the furnace is heated to a carburizing temperature that is between the transformation temperature of the piece of metal and approximately 2000xc2x0 Fahrenheit. Next, the piece of metal is placed into the furnace while heated to the carburizing temperature and filled with the carburizing gas mixture. Finally, the piece of metal is removed from the furnace after approximately 5 to 15 minutes.
In preferred embodiments of the above: the carburizing gas mixture is controlled such that the carbon-rich gas accounts for approximately 2 to 4% of the mixture by mass; the carbon-rich gas primarily comprises methane; the piece of metal moves through the furnace on a continuous belt; the furnace is a humpback furnace; the piece of metal is comprised primarily of stainless steel; the stainless steel is 300 series stainless steel; the piece of metal is a swage mount component; the piece of metal is a component for use a hard drive HSA; and/or the carrier gas is essentially all hydrogen gas.
The invention also is directed to carburizing a piece of metal that has a transformation temperature above which annealing occurs and below which stress relief occurs. Initially, a furnace is filled with a carburizing gas mixture consisting of a carbon-rich gas and a carrier gas that is comprised primarily of hydrogen gas, and the furnace is heated to a carburizing temperature that is between the transformation temperature of the piece of metal and approximately 2000xc2x0 Fahrenheit. Then, the piece of metal is placed into the furnace while heated to the carburizing temperature and filled with the carburizing gas mixture. After approximately 5 to 15 minutes, the piece of metal is removed from the furnace. According to this aspect of the invention, the carburizing gas mixture is controlled such that the carbon-rich gas accounts for approximately 2 to 4% of the mixture by mass, and the piece of metal moves through the furnace on a continuous belt.
In preferred embodiments of the above: the carbon-rich gas is comprised primarily of methane; the furnace is a humpback furnace; the piece of metal is comprised primarily of stainless steel; the stainless steel is 300 series stainless steel; the piece of metal is a swage mount; and/or the swage mount is for use in a hard disk drive HSA.
By utilizing a carrier gas that is lighter than air, the above carburizing process often can be conducted in a continuous belt furnace, such as a humpback furnace. Thus, carburization according to the present invention often can be accomplished more efficiently than conventional techniques, while simultaneously reducing the amount of ambient air that leaks into the furnace. By utilizing a reducing gas, such as hydrogen, the buildup of oxides on the surface of the component also can be inhibited.
Nitriding Techniques
The present invention also addresses the foregoing problems in the prior art by providing nitriding techniques that can be used to more efficiently produce components for use in swage mounting, as well as various other types of components. More specifically, this aspect of the present invention generally concerns nitriding techniques, such as nitriding techniques for surface hardening a metal component.
Thus, the invention is directed to nitriding metal having a transformation temperature above which annealing occurs and below which stress relief occurs. A piece of metal is placed into a furnace which has been heated to a temperature of between 900xc2x0 Fahrenheit and the transformation temperature of the metal and which has been filled with a mixture of nitrogen-bearing gas (i.e., either N2 or a nitrogen compound gas) and a carrier gas that includes hydrogen gas. The piece of metal is then removed from the furnace after a predetermined period of time.
In preferred embodiments of the above: the furnace is a continuous furnace; the predetermined period of time is from 5 to 15 minutes; the temperature of the furnace is between 1400xc2x0 and 1600xc2x0 Fahrenheit; the mixture of nitrogen-bearing gas and the carrier gas is controlled such that the nitrogen accounts for approximately 4 to 8% of the mixture by mass; the furnace does not contain a catalyst; the metal is stainless steel; the piece of metal is a swage mount component; the piece of metal is a component for use in a hard drive HSA; the carrier gas is comprised primarily of hydrogen gas; and/or the carrier gas is comprised essentially entirely of hydrogen gas.
The invention also is directed to nitriding metal having a transformation temperature above which annealing occurs and below which stress relief occurs. A piece of metal is placed into a furnace which has been heated to a temperature of between 900xc2x0 Fahrenheit and the transformation temperature of the metal and which has been filled with a mixture of nitrogen gas and a carrier gas that includes hydrogen gas. The piece of metal is removed from the furnace after a predetermined period of time. According to this aspect of the invention, the mixture of nitrogen gas and hydrogen gas is controlled such that the nitrogen accounts for approximately 4 to 8% of the mixture by mass, in one embodiment, or approximately 20% in another embodiment.
In preferred embodiments of the above: the furnace is a continuous furnace; the predetermined period of time is from 5 to 15 minutes; the temperature of the furnace is between 1400 and 1600xc2x0 Fahrenheit in one embodiment or approximately 2000xc2x0 Fahrenheit in another; the furnace does not contain a catalyst; the metal is stainless steel; the metal is series 300 stainless steel; the metal is austenitic stainless steel; the piece of metal is a swage mount component; the piece of metal is a component for use in a hard drive HSA; the carrier gas is comprised primarily of hydrogen gas; and/or the carrier gas is comprised essentially entirely of hydrogen gas.
The invention also is directed to nitriding a piece of metal by placing it into a furnace which has been heated to a temperature of between approximately 1400 and 1600xc2x0 Fahrenheit and which has been filled with a mixture of HSA and a carrier gas that includes hydrogen gas, with the mixture being controlled such that the nitrogen accounts for approximately 4 to 8% of the mixture by mass. The piece of metal is removed from the furnace after approximately 5 to 15 minutes.
In preferred embodiments of the above: the furnace does not contain a catalyst; the metal is stainless steel; the metal is series 300 stainless steel; the metal is austenitic stainless steel; the piece of metal is a swage mount component; the piece of metal is a component for use in a hard drive HSA; the carrier gas is comprised primarily of hydrogen gas; and/or the carrier gas is comprised essentially entirely of hydrogen gas.
By utilizing HSA when nitriding in the foregoing manner, the present invention often can avoid the need to dispose of non-dissociated ammonia gas, which is a common problem in conventional techniques. As a further benefit, use of a catalyst often can be omitted in the foregoing arrangements.
In more particularized aspects of the invention, the carrier gas is primarily, or essentially all, hydrogen gas. As a result, buildup of oxides on the surface of the metal often can be significantly inhibited.
Comments on the Summary
The foregoing summary is intended merely to provide a quick understanding of the general nature of the present invention. A more complete understanding of the invention can only be obtained by reference to the following detailed description of the preferred embodiment in connection with the accompanying drawings.